1. Field of the Invention
The present invention relates to a liquid ejection head for use in a liquid ejection apparatus in which a liquid, such as an ink, is ejected through an ejection orifice to form a liquid droplet for recording an image, and a method of manufacturing the liquid ejection head. The liquid ejection head of the present invention can be applied to not only general ink jet recording apparatuses, but also to other various types of apparatuses, such as copying machines, facsimiles including communication systems, and word processors including recording units, including industrial recording apparatuses combined with various processors.
2. Description of the Related Art
In recording apparatuses such as printers, copying machines and facsimiles, an image made up of dot patterns is recorded on a recording medium in accordance with image information. From a point of recording method, those recording apparatuses can be divided into the ink jet type, the wire dot type, the thermal type, the laser beam type, and so on. Among them, a recording apparatus of the ink jet type includes an ink jet head in which liquid passages are formed. An energy conversion unit for generating ejection energy utilized to eject a liquid, i.e., ink, is provided in each liquid passage in the head, and the ink is introduced to the liquid passage from an ink supply port through a liquid chamber. In the liquid passage, the ejection energy is applied to the ink, whereupon the ink flies in the form of a droplet toward a recording medium. An image is recorded on the recording medium with the ink droplet impinging against the recording medium. Of various types of ink jet heads, one utilizing thermal energy to eject an ink has been widely practiced because of having advantages in that ink ejection orifices, through which an ink droplet for recording is ejected in the form of a flying droplet, can be arrayed at a high density and the head can be easily constructed in compact size as a whole. Further, in recent years, the number of nozzles arrayed in the ink jet head has increased to meet an increasing demand for recording at a higher rate.
In the ink jet head, however, because ink in the liquid phase is handled, the meniscus vibration in an ejection nozzle is noticeably disturbed due to ink vibration and image quality is sometimes deteriorated. Particularly, in an ink jet head having a large number of nozzles arrayed at a high density, because an ink is moved through a relatively large distance per unit time, a greater inertial force is imposed on the ink in a tank system and moves it forward (toward the head side) when the ejection operation is stopped. With such a greater inertial force, a positive pressure is applied to an ink flow passage, thus bringing the meniscus into a protruded condition. If a next recording signal is inputted in that condition, there occurs the so-called splash printing in which small ink droplets are scattered.
FIG. 17 is a chart showing a waveform of pressure vibration in an ink flow passage responsive to ejection pulses applied to perform one predetermined cycle of ejection in an ink jet head, and FIGS. 18A to 18C are sectional views of a nozzle showing respective meniscus states during a period A (before start of the ejection), a period B (during the ejection), and a period C (immediately after stop of the ejection) denoted in FIG. 17. As seen from FIG. 17, the pressure vibration in the flow passage has a large amplitude a immediately after stop of the ejection. A positive pressure, therefore, occurs in the flow passage and disturbs the meniscus vibration in the next cycle of ejection. More specifically, during the period A denoted in FIG. 17, a stable meniscus M is formed as shown in FIG. 18A. When the ejection operation (pulse energization of a heater 353) is performed in that condition during the period B, a satisfactory liquid droplet 350 is ejected as shown in FIG. 18B. When the operation enters the period C immediately after stop of the ejection, the pressure in a liquid flow passage 352 is increased due to the inertia of liquid movement toward an ejection orifice 351, thus giving rise to a positive pressure in the liquid flow passage 352. The meniscus M is thereby formed in a condition protruding from a surface, in which the ejection orifice 351 is formed, as shown in FIG. 18C. In the worst case, the ink is dropped from the ejection orifice 351. Accordingly, if the next cycle of ejection is started in the condition of FIG. 18C, small ink droplets are scattered and an image cannot be formed in a satisfactory way as mentioned above.
To overcome such a problem, it has been proposed to suppress the meniscus vibration through adjustment of the flow resistance by changing the filter diameter or the ink flow passage. However, setting the flow resistance to a larger value raises a problem in that ink refill to an ejection nozzle is not performed in time and a sufficient amount of ink is not ejected, which causes a deficiency of ink density. On the other hand, setting the flow resistance to a smaller value raises another problem in that, although the ink refill can be performed in time, the amplitude of the meniscus vibration cannot be suppressed and the range of optional matters in design is restricted.
One object of the present invention is to provide a liquid ejection head, which can suppress a deterioration of liquid ejection characteristics caused by a liquid vibration upon ejection of a liquid, and to provide a method of manufacturing the liquid ejection head.
Another object of the present invention is to provide a liquid ejection head comprising a plurality of opened liquid flow passages arranged side by side and communicating with ejection orifices through which a liquid is ejected, thermal energy generating elements for generating thermal energy utilized to eject the liquid through the ejection orifices and generating bubbles in the liquid, and movable members arranged in an opposed relation to the thermal energy generating elements and having free ends displaceable upon generation of the bubbles, the thermal energy generating elements and the movable members being arranged respectively in the plurality of opened liquid flow passages, wherein at least one closed liquid flow passage closed at one end corresponding to the ejection orifice is provided in at least one end side of the plurality of opened liquid flow passages in a direction in which the opened liquid flow passages are arranged.
In the liquid ejection head having the above features, at least one closed liquid flow passage closed at one end corresponding to the ejection orifice is provided in at least one end side of the plurality of opened liquid flow passages communicating with the ejection orifices. Since the closed liquid flow passage is closed at one end corresponding to the ejection orifice and is not communicated with open air, the liquid is relatively hard to flow into the closed liquid flow passage. Accordingly, a bubble is formed to extend from the interior of the closed liquid flow passage rearward, i.e., toward the other end side of the closed liquid flow passage opposite to the side of the ejection orifices communicating with the opened liquid flow passages. The formation of a bubble means that a buffer capable of absorbing a liquid vibration caused upon ejection of the liquid is formed in the liquid ejection head. As a result, vibrations of liquid meniscuses at the ejection orifices can be suppressed.
In the liquid ejection head of the present invention, the closed liquid flow passage may be provided in both end sides of the plurality of opened liquid flow passages. Also, the liquid ejection head of the present invention may include an ejection orifice plate joined to an end surface of a head body comprising an element substrate in which the thermal energy generating elements are formed, and a top plate joined to the element substrate in an opposed relation, the ejection orifice plate having the ejection orifices formed in positions corresponding to the opened liquid flow passages. The top plate may have a reinforcing portion provided corresponding to the closed liquid flow passage and having one flat surface flush with the end surface of the head body. Further, the reinforcing portion may have a size enough to block off communication between the closed liquid flow passage and an outside. In that case, since the reinforcing portion has one flat surface flush with the end surface of the head body at which the head body is joined to the ejection orifice plate, a joining surface of the ejection orifice plate to the head body is increased in amount equal to one flat surface of the reinforcing portion in flush with the end surface of the head body. As a result, the joining strength of the ejection orifice plate can be increased to a more reliable level.
Still another object of the present invention is to provide a liquid ejection head comprising a plurality of opened liquid flow passages arranged side by side and communicating with ejection orifices through which a liquid is ejected, thermal energy generating elements for generating thermal energy utilized to eject the liquid through the ejection orifices and generating bubbles in the liquid, and movable members arranged in an opposed relation to the thermal energy generating elements and having free ends displaceable upon generation of the bubbles, the thermal energy generating elements and the movable members being arranged respectively in the plurality of opened liquid flow passages, wherein a plurality of closed liquid flow passages closed at one ends corresponding to the ejection orifices are provided in at least one end side of the plurality of opened liquid flow passages in a direction in which the opened liquid flow passages are arranged, and a flow resistance is provided only in a part of the plurality of closed liquid flow passages on the side near the opened liquid flow passages.
The flow resistance may be a movable member similar to that provided in the opened liquid flow passage. When energy is applied to the energy generating element to generate and grow a bubble in a condition where the liquid is present in the liquid flow passage provided with the flow resistance in the form of a movable member, the presence of the movable member suppresses a back wave, i.e., a pressure wave, which is produced in the liquid flow passage provided with the flow resistance upon generation of the bubble and is moved toward the rear side of the liquid flow passage provided with the flow resistance. Therefore, the movement of the bubble toward the rear side of the liquid flow passage provided with the flow resistance is also suppressed. It is hence possible to prevent an ejection failure from occurring upon the bubble entering the liquid flow passage which is adjacent to the liquid flow passage provided with the flow resistance and contributes to the liquid ejection.
Still another object of the present invention is to provide a liquid ejection head comprising a plurality of opened liquid flow passages arranged side by side and communicating with ejection orifices through which a liquid is ejected, and thermal energy generating elements for generating thermal energy utilized to eject the liquid through the ejection orifices and generating bubbles in the liquid, the thermal energy generating elements being arranged respectively in the plurality of opened liquid flow passages, wherein a plurality of closed liquid flow passages closed at one ends corresponding to the ejection orifices are provided in at least one end side of the plurality of opened liquid flow passages in a direction in which the opened liquid flow passages are arranged, and a flow resistance is provided only in a part of the plurality of closed liquid flow passages on the side near the opened liquid flow passages.
Still another object of the present invention is to provide a method of manufacturing a liquid ejection head comprising the steps of preparing a body of the liquid ejection head, which comprises a plurality of liquid flow passages arranged side by side and communicating with holes at one ends thereof, and thermal energy generating elements for generating thermal energy utilized to eject a liquid through ejection orifices communicating with the holes and generating bubbles in the liquid, the thermal energy generating elements being arranged respectively in the plurality of liquid flow passages; and joining the body of the liquid ejection head and an ejection orifice plate having the ejection orifices formed therein in number less than the number of the holes to each other such that communication is maintained between a part of the holes and the ejection orifices, whereby the plurality of flow passage are divided into opened liquid flow passages communicating with the ejection orifices and closed liquid flow passages which are closed by the ejection orifice plate at one ends corresponding to the ejection orifices and are provided in at least one end side of the plurality of opened liquid flow passages in a direction in which the opened liquid flow passages are arranged.
In the liquid ejection head of the present invention, at least one closed liquid flow passage closed at one end corresponding to the ejection orifice is provided in at least one end side of the plurality of opened liquid flow passages communicating with the ejection orifices. Since the closed liquid flow passage is closed at one end corresponding to the ejection orifice and is not communicated with open air, the liquid is relatively hard to flow into the closed liquid flow passage. Accordingly, a bubble having the function of absorbing a liquid vibration caused upon ejection of the liquid is formed to extend from the interior of the closed liquid flow passage rearward. As a result, vibrations of liquid meniscuses at the ejection orifices can be suppressed, and an adverse effect upon ejection characteristics can be avoided. With the method of manufacturing the liquid ejection head according to the present invention, the liquid ejection head having the above-described construction can be manufactured with ease.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.